The present invention relates to automotive vehicles, and more particularly to powertrain control of automotive vehicles.
It is known to control an engine and transmission to provide a desired torque. However, the inventors of the present invention have recognized the following items: 1) in certain instances, it is necessary to control the amount of, and provide sufficient, negative engine torque or engine braking; 2) in certain instances, it is also advantageous to provide a maximum amount of engine braking to the vehicle. Such situations may be advantageous to vehicle speed control, for example.
The inventors herein have further recognized a disadvantage with prior approaches. In particular, the inventors have recognized that it may not be possible to provide maximum engine braking unless the torque converter is locked. Further, the inventors have recognized that it is also necessary to minimize transmission gear separation and corresponding re-engagement, since this can degrade drivability. In other words, when the powertrain torque changes from positive to negative, or vice versa, gear separation can occur and transmission xe2x80x9cclunkxe2x80x9d can occur.
The disadvantages of prior approaches are overcome by a method for controlling a clutch of a torque converter interposed between and engine and a transmission. The method comprises determining whether torque converter output speed has become greater than torque converter input speed while the torque converter clutch is disengaged, and in response to said determination, engaging the torque converter clutch after torque converter output speed has become greater than torque converter input speed.
By engaging the clutch after torque converter output speed has become greater than torque converter input speed, it is possible to lock the torque converter for controlling negative torque, while at the same time minimize drivability difficulties related to passing through the transmission lash area.
An advantage of the present invention is that, if desired, it is possible to control negative powertrain torque to a desired level, and even provide a maximum level.
Another advantage of the present invention is that by locking the torque converter in the negative powertrain output region, it is possible, if desired, to provide a smooth transition through the zero torque point and thus minimize potentially degrading effects of transmission gear lash on drivability.